Method of producing low profile stent and graft combination

ABSTRACT

Large diameter self-expanding endoprosthetic devices, such as stents and stent grafts for delivery to large diameter vessels, such as the aorta, are disclosed having very small compacted delivery dimensions. Devices with deployed dimensions of 26 to 40 mm or more are disclosed that are compacted to extremely small dimensions of 5 mm or less, enabling percutaneous delivery of said devices without the need for surgical intervention. Compaction efficiencies are achieved by combining unique material combinations with new forms of restraining devices, compaction techniques, and delivery techniques. These inventive devices permit consistent percutaneous delivery of large vessel treatment devices. Additionally, small endoprosthetic devices are disclosed that can be compacted to extremely small dimensions for delivery through catheter tubes of less than 1 mm diameter.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a division of now abandoned U.S. patentapplication Ser. No. 09/235,458, filed Jan. 22, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of producing endoprostheticdevices, such as stents and stent-grafts, that are used to repair and/ortreat diseased or damaged vessels and other structures within a body,and particularly to such devices that can be introduced at smalldelivery profiles and then enlarged in place.

2. Description of Related Art

Stents and stent-grafts are used in the treatment of vascular and otherdisease. They are particularly useful for treatment of vascular orarterial occlusion or stenosis typically associated with vesselsnarrowed by disease. Intraluminal stents and stent-grafts function tohold these vessels open mechanically. In some instances, they may beused subsequent to, or as an adjunct to, a balloon angioplastyprocedure. Stent-grafts, which include a graft cover, are alsoparticularly useful for the treatment of aneurysms. An aneurysm may becharacterized as a sac formed by the dilatation of a wall or an artery,vein, or vessel. Typically the aneurysm is filled with fluid or clottedblood. The stent-graft provides a graft liner to reestablish a flowlumen through the aneurysm as well as a stent structure to support thegraft and to resist occlusion or stenosis.

Treatment of a bifurcation site afflicted with such defects as anocclusion, stenosis, or aneurysm is a particularly demanding applicationfor either stents or stent-grafts. A bifurcation site is generally wherea single lumen or artery (often called the “trunk”) splits into twolumens or arteries (often called “branches”), such as in a “Y”configuration. For example, one such bifurcation site is found withinthe human body at the location where the abdominal aorta branches intothe left and right (or ipsilateral and contralateral, respectively)iliac arteries.

When a defect, such as an aneurysm, is located very close to thebifurcation of a trunk into two branches, treatment becomes especiallydifficult. One reason for this difficulty is that neither the trunk noreither of the branches provides a sufficient portion of healthy vesselwall proximal and distal to the defect to which a straight section ofsingle lumen stent or stent-graft can be secured. The stent orstent-graft must span the bifurcation site and yet allow relativelyundisturbed flow through each of the branches and trunk.

Stents and stent-grafts offer considerable advantages over conventionalsurgery. Because they are comparatively less invasive, reduced mortalityand morbidity, combined with shorter hospital stay, are the moresignificant advantages of stent and stent-graft therapies. Low profileendoprostheses (that is, endoprostheses that can be compacted into asmall size for delivery) continue to be developed that enable theintroduction of such devices through progressively smaller holes cut orpunched through vessel walls. These low profile devices reduce bloodloss and procedural morbidity compared to higher profile devices.Preferably, low profile devices should also be more flexible in thecompacted delivery state. Devices that are more flexible during deliverybetter enable passage through tortuous vessels en route to the desireddelivery site. Furthermore, thinner walled devices may cause less flowdisturbance at the inlet and outlet to the graft.

The preferred device is one that can be introduced “percutaneously,”that is through a small transcutaneous incision or puncture 12 French(F) (4.0 mm) or less in diameter. Percutaneous delivery of a stent orstent-graft can often be done on an out-patient basis, and is typicallyassociated with decreased patient morbidity, decreased time to patientambulation, decreased procedural time, and potential reduction in healthcare delivery cost compared to surgical delivery of endoprostheses.

A “stent-graft” is formed by providing a covering on either the inside,outside, or both surfaces of the stent. These covered devices canprovide a number of improvements over conventional uncovered stents.First, the cover may provide a fluid barrier (that is, either liquid orgas or both), prohibiting transmural fluid leakage from the inside tothe outside of the device, or inhibiting transmural infiltration offluids into the lumen of the device, or both. Second, covered devicescan also limit tissue encroachment into the device over time. Third, itis believed that a covered device may provide an improved flow surface,which may aid in longer and more effective operating life for thedevice.

While covered stent devices have many benefits, unfortunately currentcovered-stents used for the treatment of disease of large vessels (e.g.,thoracic or abdominal aortic vessels) generally require a surgicalincision to provide a large enough access site to deliver such devices.Virtually all such devices currently are too large for less-invasivepercutaneous delivery.

The current standard procedure for stent and stent-graft delivery isoutlined below. The stent or stent-graft device is reduced in diameter(“compacted”) to enable it to be introduced through small incisions orpunctures via a trans-catheter approach. “Self-expanding” devicesinherently increase in diameter once a restraining mechanism is removed.“Restraining mechanisms” typically fit over part or all of the outersurface of compacted self-expanding devices to constrain them in areduced diameter on the delivery catheter until deployment. “Deployment”is the term given to increasing the diameter of these intraluminaldevices and subsequent detachment of the device from the deliverycatheter. “Deployed inner diameter” as used herein is the device innerdiameter measured immediately subsequent to releasing the device fromits restraining mechanism in a 36–40° C. water bath and pressurizing thedevice to 1 Atm with an appropriately sized balloon dilatation catheter.An appropriately sized balloon will transmit the 1 Atm pressure to thedevice. For devices that cannot withstand a 1 Atm pressure, the deployedinner diameter corresponds to the size of the device immediately priorto rupture. For devices that require balloon expansion, the appliedpressure is that pressure required to fully deploy the device to itsintended dimensions.

Once self-expanding devices are properly positioned within the body, therestraining mechanism is removed, thereby deploying and anchoring thedevice. “Balloon-expandable” devices require the use of a ballooncatheter or other means of dilatation within the recipient luminalstructure for deployment and anchoring. Such devices are typicallymounted and delivered on top of a balloon, which inherently increasestheir delivery profile.

As has been noted, percutaneous delivery is almost always preferred butis difficult or impossible to achieve for larger devices. A device(including restraining mechanism, if any) with a maximum outer dimensionof no more than 10 French (F) (3.3 mm) can almost always be deliveredpercutaneously. More skilled physicians may opt to place devicespercutaneously with dimensions of 12 F (4.0 mm), 13 F (4.3 mm), 14 F(4.7 mm), or more, although bleeding and other complications increasemarkedly with increasing access site size. Generally herein, a“percutaneous” device is considered to be a device that has an outerdiameter in a delivered state of no more than 12 F.

Devices are generally placed into the body through percutaneously orsurgically placed introducer sheaths that are sized according to theirinner diameter. The wall thicknesses of these sheaths typically addsabout 2 F to the size of the device. That is, a 12 F introducer sheathhas about a 14 F outer diameter. “French” measurements used hereindefine the size of a hole through which a device will pass. For example,device with a measurement of “10 French” will pass through a 10 Frenchhole (which has a diameter of 3.3 mm). A device need not have a circularcross-section in order to pass through a circular 10 French hole so longas the hole is large enough to accommodate the widest cross-sectiondimension of the device. The delivery size of an intraluminalstent-graft device is a function of stent geometry, stent-graftcompacting efficiency, volume of the stent, volume of the stent cover,thickness of the restraining mechanism (if any), and the outer diameterof any guidewire or catheter within the lumen of the compacted device.

There are many problems encountered in attempting to compact a deviceinto its smallest deliverable dimensions. First, the material of thestent element itself takes up a certain volume. If a graft component isadded, this further increases the bulk of the device. Accordingly, thereare absolute limits to compaction based strictly on the volume of thecomponent parts.

Second, all known stent element designs provide the stent withcrush-resistance (which is required if the stent is to have anystructural value in holding open a vessel). This resistance to crushingfurther confounds attempts to tightly compact the device—with the riskthat over-compacting the stent may damage its crush-resistance (and thusits structural value as a stent). On the other hand, less resilientstent devices might be more receptive to compaction, but are lesseffective in holding open the vessel once deployed.

Third, the graft material is also at risk of damage during compacting.Since the stent and the graft are compacted together, the stent elementmust be designed and compacted in such a way that it will not damage thegraft when the two are compressed together.

Fourth, any compaction of a stent or stent-graft will likely tend toreduce the flexibility of the compacted device. Extreme compaction mayproduce a compacted device that is so inflexible that it will notnegotiate tortuous paths in the body.

Fifth, as has been noted, currently available delivery devices andtechniques (e.g., introducer sheaths, guidewires, delivery catheters,etc.) also add bulk to the device—generally adding about 2 to 3 F (0.67to 1 mm) or more to the profile of the apparatus that must be deliveredthrough the vascular access site.

Sixth, there are covered stents available today that can be compressedinto small delivery profiles, but these devices undergo extremeelongation in their compressed state, with extreme foreshortening whentransitioned to their deployed dimensions. These extremes in devicelength between compact and deployed dimensions make these devicesdifficult to properly position and deploy. Additionally, these devicestend to have less resilient stent structures. Finally, perhaps thegreatest deficiency of these devices is that they must be covered with amaterial that can likewise undergo extreme elongation and contraction tomatch the longitudinal behavior of the stent element. As a result,preferred biocompatible graft materials such as polytetrafluoroethylene(PTFE) and woven DACRON® polyester are not readily used on these devicessince neither is capable of extreme stretching and rebounding.

Results have been reported that a braided stent graft with a highlyporous elastomeric covering allows the stent, when compacted fordelivery, to be substantially elongated. Distributing the stentcross-sectional mass over a longer length (up to 40% length change)allows percutaneous delivery of a large device. Although these devicescan fit through smaller delivery sites of 8 to 10 F, exact placement isoften difficult because of the significant longitudinal retraction orrecoil of the stent graft as it reaches its deployed size. The design ofthis stent relies on extreme elongation to achieve its compaction, henceundesirable foreshortening of the device naturally occurs duringdeployment. As a result, this design cannot accommodate a longitudinalstrength member that would resist elongation during compaction of thedevice. In order to allow the stent frame to undergo extreme changes inlength, elastomeric coverings are employed to permit the cover to expandand contract along with the stent frame. The coverings primarily serveas a barrier to the passage of blood and/or tissue or other elements inuse, although their stretch and recovery requirements severely limitthey types of materials that can be used in this device. Thickness andporosity is also a design limitation for these elastomeric stentcoverings. To reduce porosity the coverings often must be thicker (oftenabout 0.05 mm or greater), which can adversely effect delivery profile.

It should be evident from the above description that it is verydesirable to provide an endoprosthetic device that can be deliveredpercutaneously. This is especially true for an endoprosthesis thatcombines the benefits of both a stent and a graft. However, therecurrently are a number of serious constraints limiting the ability tocompact endoprosthetic devices, and particularly large vesselendoprosthetic devices (for instance, for treatment of aortic diseasesand trauma), into their smallest possible delivery profiles.

SUMMARY OF THE INVENTION

The present invention provides methods of substantially reducing thedelivery profile of endovascular devices and substantially increasingthe ratio of the deployed inner diameter and compacted outer diameter ofsuch devices.

To achieve extremely small delivery profiles, low profile devices of thepresent invention are constructed using the following techniques:exceptionally thin and strong covers (e.g., expandedpolytetrafluoroethylene and/or polyester mesh); small gauge (diameter)wire (e.g., nitinol wire) to construct stent frames or thin-walled cuttubing; stent geometry that enables a high packing efficiency; low massmeans of attaching covers to stent frames; and improved methods forcompacting stent-grafts. Furthermore, a low profile means of restrainingthe device in the non-distended (i.e., compacted) state, ready fordelivery, are also utilized in the design. Finally, improved deliverytechniques that enable the use of lower profile devices are alsoincorporated.

An important purpose of the present invention is to providepercutaneously deliverable, large diameter stent-graft devices for thetreatment of large vessel (e.g., aortic) disease. An endoprostheticdevice of the present invention can achieve extremely high compactionefficiencies, containing a stent-graft with a deployed inner diameter ofgreater than 23 mm into a compacted dimension with a diameter of lessthan 12 F. This can be achieved with minimal longitudinal length changein the device between its compacted and deployed dimensions.

Further advantages of the present invention are to provide a very lowprofile covered-stent, and to provide a covered-stent with the broadestdeployment range, from the delivery size to the fully extended (i.e.,deployed) size. Still another advantage of the present invention is theability to create very small implantable devices that are capable ofbeing delivered in extremely small compacted dimensions. These and otherbenefits of the present invention will be appreciated from review of thefollowing description.

DESCRIPTION OF THE DRAWINGS

The operation of the present invention should become apparent from thefollowing description when considered in conjunction with theaccompanying drawings, in which:

FIG. 1 is three-quarter side elevation view of a large diameter thoracicaortic stent-graft of the present invention shown in its fully deployeddimension;

FIG. 2 is a three-quarter side elevation view of a large diameterstent-graft of the present invention shown in its compacted dimensionand mounted on a delivery catheter beneath a sleeve-like restrainingmechanism;

FIG. 3 is a side elevation view of one embodiment of deploymentapparatus for use with the present invention;

FIG. 4 is a three-quarter side elevation view of a two-part, modular,large diameter bifurcated stent-graft of the present invention shown inits fully deployed dimension;

FIG. 5 is a top view of the stent-graft of FIG. 4;

FIG. 6 is a side elevation view of the stent-graft of FIG. 4 shown inits deployed orientation (i.e., with the modular components of FIG. 4joined together);

FIG. 7 is a top plan view of a stent pattern used in a thoracic aorticstent-graft shown in FIG. 1. The stent-graft is cylindrical but isrepresented in this “flat plan configuration” by making a longitudinalcut along the length of the endoprosthesis and the uncoiling of theendoprosthesis along this cut into a flat sheet;

FIG. 8 is a flat pattern configuration of the stent element that may beused to form a straight stent-graft of the present invention;

FIG. 9 is a flat pattern configuration of the stent element used to formthe trunk component of the modular bifurcated stent-graft of FIGS. 4through 6;

FIGS. 10 through 13 are side cross-section views of the steps ofdeploying a straight stent-graft of the present invention within avessel having an aneurysm, the stent-graft being deployed from a fullycompacted dimension in FIG. 10 to a fully deployed dimension in FIG. 13;

FIG. 14 is a top plan view of one embodiment of a tapered die used tocompact the stent-graft of the present invention;

FIG. 15 is a side cross-section view of the tapered die of FIG. 14 alongsection line 15—15;

FIG. 16 a is a three-quarter isometric view of another embodiment of atapered die used to establish a pleated compacted endoprosthesis of thepresent invention, this tapered die including fluting (i.e.,longitudinal ridges) to assist in compaction by forming folded pleats inthe device during compaction;

FIG. 16 b is a side cross-section view of the tapered die of FIG. 16 aalong line 16 b—16 b;

FIG. 16 c is a top plan view of the tapered die of FIGS. 16 a and 16 bshowing a circular stent-frame being drawn through the tapered die usingtether lines;

FIG. 17A is a side elevation view of a segment of a straight stent-graftof the present invention shown in its fully deployed dimension;

FIG. 17B is a side elevation view of the segment of straight stent-graftof FIG. 17A shown in its compacted dimension having been folded intopleats;

FIG. 18 is a section view of the pleated stent-graft of FIG. 17B alongsection line 18—18;

FIG. 19 is a side elevation view of a partially covered stent-graft ofthe present invention in a fully deployed dimension having tether linesattached to it for compaction through a tapered die, the tether linesbeing aligned with stent undulations all facing in the same direction;

FIGS. 20 through 22 are side elevation views of a compression fixtureused to compact a stent-graft of the present invention through a tapereddie and into a restraining sleeve, a straight stent-graft of the presentinvention being illustrated in the sequential compaction steps;

FIG. 23 is a flat pattern configuration of another embodiment of arestraining sleeve used to constrain the stent-graft of the presentinvention;

FIG. 24 is side elevation view of a restraining sleeve incorporating thepattern of FIG. 23, with the sleeve shown partially removed via anintegral, multi-filament deployment line;

FIG. 25 is a side elevation view of another embodiment of a stent-graftof the present invention being deployed in an aneurysmal, bifurcatedblood vessel shown in cross-section;

FIG. 26 is longitudinal cross-section view of the stent-graft embodimentshown in FIG. 25 illustrating a pusher mechanism for stent-graftdeployment directly from a delivery catheter without use of a guidewireor a separate restraining sleeve on the stent-graft;

FIG. 27 is a side elevation view of another embodiment of a stent-graftof the present invention being deployed in an aneurysmal, bifurcatedblood vessel shown in cross-section;

FIG. 28 is a flat pattern configuration of a stent element of thepresent invention cut from a metal tube; and

FIG. 29 is a side elevation view of another embodiment of apparatus usedto compact stent-grafts of the present invention, this embodimentemploying a two-stage tapered die.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improved endoprosthetic device, particularlysuch a device for use in large diameter vessels, that is capable ofbeing compacted into very small delivery dimensions. For instance,stent-graft endoprosthetic devices of the present invention may beformed in large deployed dimensions for thoracic aortic vessels (withdiameters of 26, 28, 30 mm or more) or for bifurcated abdominal aorticvessels (with diameters of 23, 25, 27 mm or more) that can be deliveredat very small compacted dimensions of 14 F (4.7 mm) or less. In fact,the present invention can even produce large vessel stent-graft devicesthat can be delivered percutaneously at less than or equal to 12 F (4.0mm).

Additionally, the compacting technology of the present invention alsopermits construction of extremely small devices, on the order of 4 mm orless in deployed diameter that can be delivered in a compacted dimensionof less than 3 or 2 F (1 or 0.7 mm).

FIG. 1 illustrates one embodiment of an endoprosthesis 10 of the presentinvention at its deployed dimension. This endoprosthesis 10 comprises astent element 12 and a cover 14 attached together to form a stent-graftcombination. This particular endoprosthesis 10 is designed for lining athoracic aortic vessel, for instance to treat an aneurysm therein.Typically this requires the device to have a cross-sectional diameter“a” in its deployed dimension of about 26 mm to 40 mm or more.

Current commercially available stent-graft devices used to treatthoracic aortic aneurysms of this type are delivered in compacteddimensions of about 18 F (6.0 mm) to 27 F (9.0 mm) or more. Thesecompacted dimensions are so large, that percutaneous delivery of thesedevices is difficult or impossible. Typically delivery of these largevessel endoprostheses requires a surgical cut-down to access deeper butlarger blood vessels for device insertion. Alternatively, some largevessel devices available today can be delivered at small deliveryprofiles, but these devices must undergo extreme and highly undesirablechanges in longitudinal length between compacted and deployeddimensions.

By contrast, by employing the materials and compaction techniques of thepresent invention, as described below, the present invention can bereduced to compacted dimensions small enough for percutaneous delivery.Moreover, such extreme compaction can be achieved with minimalelongation or foreshortening of the device between compacted anddeployed dimensions. FIG. 2 illustrates a stent-graft endoprosthesis 10of the present invention presented in compacted dimensions for delivery.With a self-expanding stent-graft 10, the device is contained within arestraining device 16 and mounted on delivery catheter 18. Olives 20 a,20 b are provided at the proximal and distal ends of the device asmounted on the delivery catheter to assist in holding the stent-graft inplace on the catheter and to aid in guiding the device through smallervessels.

This embodiment of the present invention employs a restraining device 16comprising a membrane 22 of material wrapped around the stent-graft 10and sewn in place with a deployment line 24. Removal of the deploymentline 24 will cause the stent-graft device to self-expand to its deployeddimension, such as that illustrated in FIG. 1.

In the compacted dimension shown in FIG. 2, the device as mounted on thecatheter has a cross-sectional diameter of “b.” With the presentinvention diameter b comprises 12 F (4.0 mm), 11 F (3.7 mm), 10 F (3.3mm), 9 F (3.0 mm), 8 F (2.7 mm), (2.3 mm), 6 F (2.0 mm) or less.Preferably the device is compacted to a diameter of 12 F or less, sothat conventional delivery apparatus can be employed and percutaneousdelivery can still be performed through an introducing sheath of 12 F orless. More preferably, the stent-graft 10 is compacted to under 9 or 8F, allowing percutaneous delivery through a 9 F delivery apparatus. Itshould be noted that while the dimension “diameter” is used herein, itshould be understood that this dimension is intended to define theeffective cross-sectional dimension of the device and is not intended tolimit the present invention to devices with circular cross-sectionalshapes.

With respect to device length, the thoracic device illustrated in FIGS.1 and 2 undergoes essentially no change between its compactedlongitudinal length “c” and its deployed longitudinal length “d.” Inthis instance, the ratio of c:d is significantly less than 1.25 (i.e.,significantly less than a 20% change in length). The endoprostheses ofthe present invention should undergo less than a 25% change inlongitudinal length between its compacted dimension and its deployeddimension. Preferably, the device will undergo less than a 20% change inlength, and even more preferably it will undergo less than a 15% or 10%change in length. Most preferably, an endoprosthesis of the presentinvention will experience less than a 5% change in longitudinal lengthbetween its fully compacted dimension and its fully deployed dimension.In this respect, the entire device as deployed is maintained compactedwithin 25% or less of its deployed longitudinal dimensions, without theneed for excessive elongation of the device in its compacted state orthe splitting of the device into multiple parts in order to achieve lowprofile delivery.

In order to achieve the small compacted dimension of the presentinvention, the first important design element is to employ uniquelow-profile materials. Cover 14 comprises a thin but strong materialthat is biocompatible, sufficiently flexible to undergo extremecompaction while returning undamaged to a fully deployed state, andsufficiently strong so as to provide proper support of the vessel wallsonce deployed. The preferred material comprises polytetrafluoroethylene(PTFE), and especially an expanded PTFE material. This expanded PTFEmaterial is described in U.S. Pat. Nos. 3,953,566, 3,962,153, 4,096,227,4,187,390, 4,902,423, and 5,476,589, all incorporated by reference.Polyester material, such as woven DACRON® polyester, may also besuitable.

The preferred expanded PTFE material for use in the present inventioncomprises a material having: a thickness of less than about 0.03 mm, andmore preferably less than about 0.004 mm; and a longitudinal matrixtensile strength of more than about 650 MPa, and more preferably morethan about 800 MPa. Layers of this material are used to create the stentcover. Note that the thickness of the cover may be less than the sum ofthe thicknesses of the individual layers because the film tends todecrease in thickness during the heat bonding process used to attach thefilm to the stent frame. “Thickness” can be measured with a snap gage oran optical comparitor, or by the use of a scanning electron micrograph.“Longitudinal matrix tensile strength” refers to the matrix tensilestrength of the material that in the direction that is parallel to thepredominant orientation of the fibrils, which corresponds to the higherstrength direction of the material. Tensile strength may be determinedusing an INSTRON tensile tester. For a porous polytetrafluoroethylene(PTFE) material, such as expanded PTFE, matrix tensile strength isdetermined as the tensile strength of the material multiplied by thequotient of the density of the PTFE polymer and the bulk density of theexpanded PTFE material. For the purpose of calculating matrix tensilestrength, 2.2 g/cc is used as the value for the PTFE polymer density.Bulk density takes into account any porosity of the expanded PTFEmaterial.

For blood conduit applications, the cover should resist the passage ofliquids under pressures of about 150 mm Hg or more. For applicationsrequiring that the cover provide exceptional liquid or gas permeationresistance (for example, a cover that may be required to resist bilepermeation), a permeability as quantified by a Gurley Number of greaterthan about 60 seconds for 1 cm² of material for 100 cc of air ispreferred, and even more preferably a Gurley Number in excess of 100seconds for 1 cm² of material for 100 cc of air; a thickness of about0.05 to 0.25 mm, with a thickness of about 0.10 to 0.20 mm preferred; awater entry pressure of about 34 to 102 kPa or more, with 48 to 62 kPaor more preferred.

The stent element 12 and the cover 14 of the present invention areadhered together (for instance, by an adhesive and/or by a wrap of anadhered film or by bonding the stent element between layers or to layersof the cover) to maintain position of the cover 14 on the endoprosthesis10. The attachment of the cover 14 to the stent element 12 alsorestricts the stent element 12 from excessively longitudinallyelongating when longitudinal tension is applied to the endoprosthesis10. It is believed preferable that the cover 14 line the interior of thestent element 12, as shown, but acceptable results may also be achievedwith the cover 14 placed on the outside of the stent element 12, withthe cover being placed both inside and outside of the stent element 12,or with the stent element 12 being embedded within the cover 14. Assuch, the term “cover” as used herein is intended to include anygenerally continuous material that is placed inside of and/or placedoutside of and/or mounted integrally with the stent element 12 of thepresent invention.

In order to achieve the lowest possible profile for the device of thepresent invention, it is very desirable that the cover 14 be attached tothe stent element 12 in such a way that the device does not becomesignificantly less flexible and the device does not have significantlymore material added to it. Although attaching the cover using a ribbonof adhered film can produce acceptable results, it is not believed to bepreferred since the film may increase the rigidity of the device, impartundesirable undulations or corrugations to the luminal surface duringbonding, and the film also adds volume to the device. Accordingly, thepreferred attachment method for joining the stent element 12 and thecover 14 is to apply layers of the cover to both the inside and outsideof the stent frame, then bonding the layers together at a temperatureabove the crystalline melt temperature of PTFE (327° C.). The luminalsurface is preferably formed to be as smooth as possible (i.e., a smoothsurface devoid of as much corrugation as possible). Alternatively,attachment may be performed by coating the stent frame with an adhesiveor applying an adhesive to the cover material, then bonding the cover tothe frame. One suitable adhesive material for these applications isfluorinated ethylene propylene (FEP).

The stent element 12 is preferably formed from a super elastic materialthat will withstand extreme compaction yet will readily return to itsoriginal dimensions without damage when unconstrained. Additionally, ifthe stent element 12 is formed from a material that will self-expand inplace, maximum compaction can be achieved since a means of dilatation orexpansion (e.g., employing a balloon catheter) need not be deliveredwithin the device in its compacted dimensions. Suitable materialsinclude alloys of stainless steel, nickel-titanium alloys (nitinol),tantalum, platinum, and titanium and rigid polymers.

The preferred material comprises a nickel-titanium alloy (nitinol) metalwire having a diameter of about 0.4 mm or less, and more preferably, adiameter of about 0.2 mm or less. For extremely small stent-grafts, awire with a diameter of about 0.1 mm or less may be preferred. Thepreferred nitinol wire comprises a nickel content of about 51% and atitanium content of about 49% (for example, SE 508 nitinol wireavailable from Nitinol Devices & Components, Fremont, Calif., USA).Additional properties that the wire may beneficially have include: atensile strength of about 1200 MPa or more; cold working of about40–45%; a tensile modulus of approximately 35 to 70×10⁶ kPa; and anelectropolished finish.

A self-expanding stent element may be formed from this material using apin-jig and following conventional procedures, such as those taught inPCT Application PCT/US96/19669 to Martin et al., incorporated herein byreference. The preferred cross-sectional shape of the stent structure isnot necessarily circular. It is possible that wire having an oval-shapedcross-section or a nitinol ribbon may be configured into an acceptabledevice. Likewise, with laser-cut tubes, there is a great deal offlexibility with cutting and polishing to achieve non-circularcross-sectional geometries.

Since the elastic properties of the stent material, the moment ofinertia of stent cross-sectional geometry and the design of the overallstent structure combine to dictate the physical characteristics of thestent, the specific strut material, cross-sectional geometry, and stentdesign may be integrally linked to given clinical applications.

By forming a device using the preferred materials of about 0.003 mmthick expanded PTFE membrane and about 0.3 mm diameter nitinol metalwire that are adhered together by heat bonding, a 40 mm diameterthoracic aortic stent-graft device, as shown in FIG. 1, can be readilycompacted down to a 3.33 mm or less diameter delivery profile, as shownin FIG. 2. As is explained in greater detail below, even further profilereduction can be achieved by employing unique folding and restrainingadvances of the present invention.

A delivery apparatus that may be used to deliver an endoprosthesis 10 ofthe present invention is illustrated in FIG. 3. This deploymentapparatus 26 comprises: an introducer sleeve 28; a restraining device16; a distal shaft 30; a proximal shaft 32; a strain relief 34; adeployment port 36; a deployment knob 38 mounted within the deploymentport 36 that is connected to a deployment line 24 attached to arestraining device 16 surrounding the endoprosthesis 10; a side armadapter 40; a flushing port 42; and a guidewire port 44. A radiopaquemarker 46 may be provided on the distal shaft 30 to aid in the remotepositioning of the endoprosthesis 10. The operation of the deploymentapparatus 26 is explained in detail below with reference to FIGS. 10through 13.

Low profile delivery of a bifurcated device, such as that employed inrepairing an abdominal aortic aneurysm (AAA), is an even morechallenging application of the present invention. The challenge in theseapplications is that an aneurysm will commonly form at the junction ofthe common iliac arteries in the abdominal aorta. In order to repairthis defect, a device ideally comprises a bifurcated structure that hasone large opening at one (proximal) end that splits into two smallerlegs at the other (distal) end. In this manner, the device can attach tothe host artery above the aneurysm and below the aneurysm in each of theiliac arteries individually, thereby excluding the aneurysmal lesionfrom the blood stream.

Although a bifurcated device is preferred for treating AAA, such deviceshave a number of inherent problems. First, the fact that a bifurcateddevice has two legs presents a placement problem when the device is tobe delivered by way of one of the iliac arteries. While the upperproximal end and one leg can be easily positioned properly around theaneurysm, the ability to then direct the other leg through the otheriliac artery can be a challenge for medical personnel. Second, thecomplexity of the bifurcated device necessarily adds a substantialamount of bulk to the device when compacted.

Numerous proposals have been made to address the first of theseproblems. One common approach is illustrated in FIGS. 4 through 6. Inthis embodiment, a bifurcated endoprosthesis 48 is provided thatincludes a trunk segment 50 having a long ipsilateral leg 52 and a shortcontralateral leg 54. The trunk segment 50 is delivered through theipsilateral iliac artery and positioned and deployed in place. Aseparate contralateral leg stent-graft segment 56 is then deliveredthrough the contralateral iliac artery and deployed to join to the shortcontralateral leg 54 on the trunk segment 50 to complete the bifurcateddevice 48. The completed device is illustrated in FIG. 6.

Even with separation of the bifurcated device into two separatelydeployable segments 50, 56, the trunk segment 50 cannot be compactedinto small enough dimensions for percutaneous delivery (although thecontralateral leg segment 56 typically can be compacted usingconventional methods from deployed dimensions of about 8 to 16 mm indiameter down to compacted dimensions of about 4 to 5 mm in diameter).Typically the trunk segment 50 will have a deployed large proximalopening 58 measuring about 20 to 36 mm in diameter (“a”) and a smalldistal opening 60 on the ipsilateral leg 52 measuring about 8 to 16 mmin diameter. Currently, this trunk segment 50 is delivered at a diameterof about 18 F (6.0 mm)—entirely too large for percutaneous delivery.

However, the device 48 may be constructed from a stent frame 62employing the 0.3 mm nitinol wire previously described, with a cover 64constructed from the 0.003 mm thick expanded PTFE membrane previouslydescribed. Joining the stent frame and cover together via heat bondingproduces a low profile stent-graft of the present invention. Employingthe low profile materials previously described, the trunk segment 50,having a proximal opening 58 of about 31 mm in diameter and a distalopening 60 of about 13 mm in diameter, can be reduced to a compacteddimension of 10 F (3.33 mm) or less. The total cover thickness, formedfrom multiple film layers, is preferably less than about 0.02 mm andmore preferably about 0.013 mm or less.

The preferred winding patterns for the various stent elements of thepresent invention are illustrated in FIGS. 7 through 9. FIG. 7illustrates (in flat orientation) a winding pattern 66 for a thoracicaortic endoprosthesis shown in FIG. 1. In this instance the stentelement 12 comprises an undulated wire having a series of forward facingapices 68 and rearward facing apices 70. As will be appreciatedfollowing review of the compaction techniques discussed below, it ispreferred that the apices 68, 70 of each row are in phase with theapices in neighboring rows. For instance, the forward facing apices 68in row 72 a are directly in phase with the forward facing apices 68 ofrows 72 b and 72 c. This winding pattern includes two longitudinalstruts 74 a, 74 b to aid in maintaining the longitudinal length andcolumn stiffness of the endoprosthesis.

FIG. 8 illustrates (again in flat orientation) a winding pattern 76 fora stent element used in a straight dimensioned endoprosthesis. Again,forward facing apices 78 and rearward facing apices 80 are in phase withneighboring forward and rearward facing apices.

FIG. 9 illustrates (again in flat orientation) a winding pattern 82 forthe proximal end of the trunk segment 50 of the bifurcated graft shownin FIGS. 4 through 6. Again, within the constraints of this morecomplicated winding pattern, the forward facing apices 84 and rearwardfacing apices 86 are essentially in phase with neighboring forward andrearward facing apices.

While these winding patterns are preferred for the various describedorientations, it should be appreciated that the exact pattern used maybe application and material specific. Accordingly, the present inventionis not intended to be limited to the winding patterns illustrated.

The process for deploying an endoprosthesis of the present invention isillustrated in FIGS. 10 through 13. In this instance a straight tubeendoprosthesis, similar to the one illustrated in FIGS. 1 through 3, isbeing deployed in a vessel 88 having an aneurysm 90 therein.

Initially, a small incision is formed through the patient's skin at asite remote from the aneurysm, for instance to expose and access thefemoral artery at the patient's groin. Using the deployment apparatusillustrated in FIG. 3, the delivery catheter 18 is passed through thepatient's skin into the femoral artery via an indwelling introducersheath. The introducer sheath is left in place through the skin andarterial wall to hold open this access site and provide a conduit intoand out of the patient for insertion and withdrawal of theendoprostheses and other tools of the physician. Ultimately, it is theouter diameter of the introducer sheath that determines whether theprocedure can be performed percutaneously. Most commercially availableintroducer sheaths have a wall thickness of about 1 F (0.33 mm), addingabout 2 F (0.67 mm) to the diameter of the access site. Accordingly, a10 F compacted endoprosthesis will require about a 12 F access site forintroduction using conventional introducer sheaths.

The endoprosthesis 10, confined in restraining device 16 and mounted onthe delivery catheter shaft 18, can be negotiated through the variousblood vessels until it is positioned within the aneurysm 90, asillustrated in FIG. 10. Positioning of the device 10 in the vessel 88can be directed using a fluoroscope or similar device. Radiopaque marker46 can be used to aid in precise positioning of the device.

Once properly positioned, the restraining device 16 can be removed byactuating deployment line 24. This will allow the self-expanding device10 to progressively enlarge in place, as shown in FIGS. 11 and 12. Oncethe restraining device 16 is completely opened or removed, theendoprosthesis 10 will be fully deployed, completely spanning theaneurysm 90, as is illustrated in FIG. 13. The delivery catheter 18 canthen be removed. At this stage the device 10 can be further enlargedusing a balloon catheter (which may be used to assure proper anchorageand smooth any wrinkles that may have formed during deployment).Following any subsequent procedures, all tools and delivery apparatus,including the introducer sheath, are removed and the access site issealed.

It is preferred to compact the endoprostheses of the present inventionthrough a funnel-shaped tapered die 92, such as that illustrated inFIGS. 14 and 15. The die 92 has a large opening 94 at one end and aninternal taper 96 leading to a much smaller opening 98 at the oppositeend. Preferably the large opening 94 is sized to be larger than thedeployed dimension of the endoprosthesis. The taper 96 is preferably setat an angle 100 of approximately 5 to 45°. The smaller opening should beapproximately the final desired compacted dimension of theendoprosthesis. The process for compacting an endoprosthesis throughsuch a die 94 is explained in greater detail below in reference to FIGS.19 through 22.

Compacting through a smooth tapered die 92, such as that illustrated inFIGS. 14 and 15, provides very good results. However, compacting in thismanner tends to produce random folds within the compacted device.Moreover, the orientation of the forward-facing and rearward-facingapices of the stent tends to be random and disorganized. The presentinventors have determined that far more effective and extensivecompaction can be achieved if the process of folding the endoprosthesisinto its compacted dimension is more carefully controlled. Inparticular, it has been determined that optimal compaction of someendoprostheses can be achieved by folding into evenly spaced pleats.

FIGS. 16 a through 16 c illustrate a modified tapered die 102 that isdesigned to provide pleated folds into an endoprosthesis. This die 102again includes a large opening 94 at one end and an internal taper 96,and a small opening 98 at its opposite end. However, in this die 102 anumber of raised flutes (or ridges) 104 are provided within the tapereddie separated by grooves 106. The raised flutes 104 and/or the grooves106 may be formed by molding or machining the shapes into the die 102.Alternatively, as is illustrated, the flutes 104 may be formed byforming evenly spaced bands 108 wound around the tapered die 102, suchas by using nylon filament with a diameter of about 0.38 mm. Regardlessof how the flutes 104 are formed, each raised flute 104 preferablycorresponds to one desired pleat to be formed in the endoprosthesis.Additionally, the flutes may be configured to be free-floating withinthe lumen of the tapered die so as to allow lateral movement of theflute as an endoprosthesis is drawn through it. This, for example, maybe achieved by fixing the radial position of the flutes at the inlet tothe die 94, but not restricting the radial position of the flute throughthe remainder of the die lumen. Alternatively, lines may be attached tothe endoprosthesis prior to drawing and removed subsequent tocompaction.

A stent or stent-graft is pulled through the tapered die by tying aseries of tether lines around the circumference of the stent. When usinga fluted, tapered die 102 precise pleat placement can be achieved bytying the tether lines to the portions of the stent that are to befolded outward. When pulled through the fluted, tapered die, the tetherlines will self-align with the grooves in the die (thus foldingoutwardly) while the untethered portions of the stent will pass over theflutes (thus folding inwardly).

This process is illustrated in the single stent ring 110 being drawnthrough the tapered die 102 by tether lines 112 in FIG. 16 c. As can beseen, the tether lines 112 have aligned with grooves 106, folding thestent ring 110 outwardly, while the untethered portions of the stentring 110 are drawn over the flutes 104 and are being folded inwardly.

As is illustrated in FIGS. 17A, 17B, and 18, a stent-graft implantabledevice 114 formed in this manner will pass from a deployed dimension “a”to a pleated compacted dimension “b.” Since the tether lines can directwhere the folds will occur, this folding technique can be used to directall of the forward facing apices 116 a in the stent frame to foldinwardly. In the folded orientation of FIG. 17B, all the forward facingapices 116 a have been folded beneath the outer surface of the compacteddevice while the rearward facing apices 116 b have been folded to theouter surface of the compacted device into pleats 118. This kind ofcontrol of folding is believed to be very beneficial to maximize foldingefficiencies by increasing the density of the compacted endoprosthesis.Additionally, it has been found that it is sometimes beneficial to haveexposed apices of a stent all facing in only one direction (that is,only the rearward facing apices 116 b are exposed in FIG. 17B). In thisway, the folded device is less likely to catch on biological structures(such as plaque and side branches), restraining sleeves, deploymentlines, and other devices that may be pulled over the compacted stent.

The advantage of forming a stent frame with all of the forward andrearward facing apices in phase with one another should now be evidentfrom the above description. By keeping the apices in phase, pleats canbe formed that will direct all of the apices of one orientation into orout of the compacted devices. Additionally, by employing in-phaseapices, greater compaction is achievable (since all of the apices willfold and compact in the same direction).

It should be appreciated that the pleated folding methods describedherein can be used to direct apices into a wide variety of foldedpatterns. As such, the terms “forward” and “rearward” facing apices areused only for convenience to describe sets of apices that face in onedirection or an opposite direction, without regard to the actualdirection the device may ultimately be deployed.

FIG. 19 illustrates a partially covered stent-graft 120 being preparedfor compacting through a tapered die. In this instance the stent-graft120 comprises a device with covered segment 122 and an uncovered segment124. The tether lines 112 are attached to either end of the stent frame126 in an evenly spaced manner. In this instance the tether lines 112are aligned with rearward facing apices 128 a, 128 b, 128 c (which areintended to remain exposed). The tether lines 112 may be formed fromthin wires, polymer fibers, or other suitable materials. The tetherlines 112 are joined together to form a termination such as a knot (orcuff) 130.

One apparatus 132 suitable for compacting endoprostheses through atapered die is illustrated in FIGS. 20 through 22. The apparatus 132comprises a jig 134 for holding a tapered die 92 and a restrainingdevice 16, and an actuation mechanism 136, in this example a screw drive138 actuated by a motor 140.

A stent or stent-graft device 142, with tether lines 112 attached, isthen oriented by large opening 94. Tether lines 112 are then passedthrough the die 92 and the restraining device 16, and attached to theactuation mechanism 136 at post 144, as is shown in FIG. 21. Onceattached, the actuation mechanism is used to draw the stent-graft 142through the tapered die 94 and into the restraining device 16 using aconstant rate of translation, or, alternatively, a constant tensileforce applied to the tether lines. The device is preferably pulledthrough the die at a low rate, such as 200 mm/min or slower. After thestent-graft device 142 has been compacted into the restraining device16, the tether lines 112 can be removed and the compacted device canthen be mounted on a catheter and otherwise packaged and prepared fordelivery. Alternatively, the device can be compacted directly onto acatheter.

It has been found that significantly smaller compacted dimensions can beachieved if the endoprosthesis undergoes repeated compressions through aseries of progressively smaller tapered dies. It is believed that anadditional reduction in compacted size can be achieved simply by passingthe endoprosthesis through a series of 2 or more, preferably 3 to 6,tapered dies of progressively smaller dimensions. As long as excessivecompaction is not attempted, this process does not appear to damage theendoprostheses. Drawing the endoprosthesis repeatedly through asame-sized die can also enable the device to be subsequently drawnthrough an even smaller die. This technique can reduce the profile by 1to 2 F or more.

The restraining device 16 used to contain the self-expandingendoprostheses of the present invention may also be reduced in profileto aid in reducing the ultimate compacted dimension of the presentinvention. With respect to the membrane restraining device previouslydiscussed and illustrated in FIG. 2, the overall thickness of themembrane may be reduced to its absolute minimum dimensions. For example,the preferred restraining means will have a thickness of 0.07 mm orless, and more preferably 0.025 mm or less.

Another approach is to employ a releasable thread as the restrainingdevice 16. For instance, FIGS. 23 and 24 illustrate a series of threads146 a, 146 b, 146 c, and 146 d that are formed into a warp knit 148around a device 150. This form of containment device is disclosed inU.S. patent application Ser. No. 09/098,103, filed Jun. 15, 1998, toArmstrong et al., incorporated herein by reference. By releasing onethread of the warp knit 148 at one end of the device (for example,thread 146 a), the entire restraining device will unravel and separateas a cohesive deployment line 152, as is shown in FIG. 24. This form ofrestraining device has proven very effective at both containing aself-expanding stent element and releasing it as an entire unit.Moreover, this form of restraining device adds minimal profile to thecompacted device. Although not preferred, another device employingthreads to contain an endoprosthesis with minimal profile increase isdisclosed in U.S. Pat. No. 5,405,378 to Strecker, also incorporated byreference.

Still another embodiment of a device for containing the compacted stentis illustrated in FIGS. 25 through 27. When deploying therapeuticdevices into the vessels of the human body conventional techniquesentail starting the procedure with a standard guidewire to traversetortuous bends and or obstructions. Once the guidewire is directed tothe desired destination in the vessel, a catheter such as a guidingcatheter or introducer sheath is coaxially inserted over the guidewireand advanced to the treatment site. At this point in the procedure, asdepicted in FIG. 25, the clinician could remove the guidewire and deploya device through the catheter, advance a device delivery catheterthrough the indwelling catheter or replace the initial guidewire with asmaller guidewire. The smaller guidewire is frequently used in order totraverse a small vessel side branch or obstructive lesion and delivertherapeutic devices. The use of smaller guidewires has the added benefitof allowing the use of even lower profile devices since the lumen of thestent or stent-graft can be reduced further during packing.

It is maintained that even smaller profile devices can be introducedshould the need for a guidewire be obviated. Such is the case should thefollowing procedure be followed: introduce a guidewire past the site tobe treated, coaxially position a long introducer sheath or catheter tothe end of the guidewire, remove the guidewire, advance the compactedstent or stent-graft beyond the end of the introducer sheath by pushingit with means such as a wire, and deploy the stent or stent-graft. Thisprocedure affords the ability to compact stents or stent-grafts to theextent that no appreciable lumen exists in the compacted state. Thisfurther reduction in profile, although minimal, can be enough to converta surgical procedure to a percutaneous procedure.

One device allowing for such a procedure is illustrated in FIGS. 25 and26. In this embodiment an endoprosthesis 154 is compacted directly intoa long introducer sheath 156, with the introducer sheath 156 servingboth as a means of directing the endoprosthesis to the treatment siteand as the restraining device used to hold the endoprosthesis in itscompacted dimension until deployment. As is shown in FIG. 26, a pushermechanism 158 may be directed through the introducer sheath 156 to pushthe endoprosthesis out of the tube and deploy it in place. This form ofdeployment apparatus can save significant compacted profile byeliminating the need for a guidewire and/or a separate restrainingsleeve on the stent or stent-graft.

FIG. 27 demonstrates that the same constraint mechanism shown in FIGS.25 and 26 can be combined with other restraining devices 160, such asthe knitted restraining device illustrated in FIGS. 23 and 24, toprovide for delivery in distinct phases. In this instance a firstsegment 162 of the endoprosthesis 154 deploys when pushed from theintroducer sheath 156 while a second segment 164 remains contained byrestraining device 160. Restraining device 160 can be separately removedwhen desired by actuating deployment line 166.

By way of summary, the present invention employs a series of techniquesthat combine to reduce the delivery profiles of stent-graft devices.These techniques include:

Thin, Strong Coverings:

Thin, strong expanded PTFE and/or polyester materials are employed toreduce the mass and volume of the stent covering. In the case of the useof expanded PTFE films, the profile is significantly reduced by creatinga circumferentially and longitudinally strong cover by applying veryhigh strength films directly to the stent frame. Other thin, strongbiomaterials may also be used in the present invention, including butnot limited to fluoropolymer elastomeric materials and polyurethanes.

Thin, Strong Stent Frames (Wires and Cut Frames):

Nitinol is used because of its superior strength, super elasticity, andbiocompatibilty. Alternative materials including, but not limited to,tantalum, titanium and stainless steel may also be used.

High Packing Efficiency Stent Frame Design:

Nitinol wire stent-frames are formed utilizing a construction thatenables a very high degree of compaction because of: nesting of in-phaseapices; sliding of the apices over top of one another upon compaction toease the compaction process; and facilitating folding efficiency of thematerial.

Improved Method of Attaching Cover Material to Stent Frame:

Bonding of the graft covering to the stent is accomplished using aslittle additional material as possible. In many cases, the expanded PTFEmaterial is simply heat bonded together. For examples in which the stentframe is covered with, but not encapsulated by, expanded PTFE material,the stent frame is first prepared by applying a very thin coating of FEPpowder. Other bonding techniques may employ coating the stent frame bydipping it in FEP dispersion, using expanded PTFE film containing eithera continuous or discontinuous layer of FEP, or using another suitablebonding agent.

Improved Stent-graft Packing Techniques:

For a given stent-graft design, it was unexpectedly learned thatrepeated pulls of the devices through the same sized smooth dies enableda further reduction in compacted profile. Furthermore, a fluted tapereddie enables even greater compaction by producing an efficientstent-graft folding pattern.

Low Profile Restraining Methods:

The delivery profile is further reduced by drawing down a delivery tubeto obtain a strong, thin-walled means of restraining the stent-graft inthe compacted state. Alternatively, a delivery tube constructed fromknitted threads that unravel when pulled from a line extending outsidethe body can be used as a low profile restraining cover.

Delivery Techniques:

Delivery techniques, such as using an introducer sheath and a pushermechanism, can be employed to further reduce the profile of compacteddevices to be introduced.

Individually, each of these techniques results in a measurable decreasein profile when applied to stent-grafts. The combination of theseproperties provides dramatic improvements in delivery profiles.Referring again to FIGS. 1 and 2, an endoprosthesis of the presentinvention having a deployed dimension of “a” in cross-section diameterand a compacted dimension of “b” in cross-section diameter is capable ofachieving dramatic ratios of expansion. For example, a conventional 40mm aortic stent-graft with limited foreshortening might achieve a ratioof a:b of 3.5:1 to 5:1. By contrast, a 40 mm stent-graft endoprosthesisof the present invention can achieve ratios of a:b of at least 7:1 upthrough 8:1, 9:1, 10:1, 11:1, 12:1, 13:1 and 14:1 or more.

As has been explained, this can lead to a device that is capable ofachieving a deployed dimension of 23 mm or more (and preferably 26, 28,30, 32, 34, 36, 38, 40, 42 mm or more) in cross-sectional diameter thatcan be reduced to a compacted dimension of 12 F or less (and preferablyless than 11 F, 10 F, 9 F, 8 F, 7 F, 6 F, or less).

As has further been explained, the compacting technology of the presentinvention also permits construction of extremely small devices, on theorder of 4 mm or less in deployed diameter that can be delivered in acompacted dimension of less than 3 or 2 F (1 or 0.7 mm). These verysmall devices possess a:b ratios of 2:1, 3:1, 4:1, 4.5:1, and 5:1, ormore.

Equally important the stent-grafts of the present invention achievesubstantial compaction with minimal change in length between theenlarged deployed dimension and the compacted dimension. As a result,the device can be accurately positioned and deployed. Additionally, thelack of significant foreshortening of the stent element allows morepreferred cover materials to be used, such as expanded PTFE and wovenpolyester, that are not capable of undergoing substantial elongation andcontraction. As has been noted, the endoprostheses of the presentinvention should undergo less than a 25% change in longitudinal lengthbetween its compacted dimension and its deployed dimension.Progressively desirable the device will undergo less than a 20%, 15%,10%, 5%, 4%, 3%, 2%, 1% or less change in longitudinal length betweenits fully compacted dimension and its fully deployed dimension.

The consistent length of the present invention is achieved through thecombination of materials and structures defined herein. Among the highlyeffective methods of preventing elongation or foreshortening of thedevice during compaction or deployment are: to employ stent elementpatterns that will naturally resist change in longitudinal length whencompacted; to use relatively inelastic cover material; and to employlongitudinal structural elements, such as struts 74 shown in FIG. 7 orlongitudinally applied (relatively inelastic) tapes or similarstructures, to resist longitudinal changes in device length.

Without intending to limit the scope of the present invention, thefollowing examples illustrate how the present invention can be made andpracticed:

EXAMPLE 1

A 40 mm inner diameter thoracic aortic stent-graft is created. The stentportion is built using 0.30 mm diameter, 40–45% cold worked NiTi(nitinol) wire (SE 508; Nitinol Devices & Components, Fremont, Calif.)formed using a mandrel with protruding pins. The stent is constructedusing a single wire, creating an undulating, helical, tubular stentmember by winding the wire on a pin fixture as described in theabove-mentioned published PCT patent application. See FIGS. 7 through 9.

Once the wire is formed on the pin fixture, it is heat treated in aconvection oven set at 450° C. for 15 minutes. After removal from theoven and quenching in a water bath, the wire frame is unwound from thefixture creating a freestanding tubular stent frame.

The stent cover is constructed from a strong, thin film. A suitable filmcomprises expanded PTFE (ePTFE) film made in accordance with theteachings of U.S. Pat. No. 5,476,589 to Bacino, incorporated byreference. This expanded PTFE “cover film” material is chosen for itsbiocompatibilty, strength, and thinness. The preferred materialpossesses a matrix tensile strength of about 900 MPa in its highstrength (longitudinal) direction a thickness of about 0.003 mm, and adensity of less than about 0.8 g/cc and more preferably between about0.15 to 0.4 g/cc. Matrix tensile strength is determined with an INSTRONtensile testing machine, using pneumatic cord and yarn grip jaws, a 25.4mm wide sample, a 102 mm jaw separation distance, and a crosshead speedof 200 mm/minute.

A 28 mm inner diameter ePTFE tube possessing a wall thickness of about0.10 mm and a density of about 0.5 g/cc is stretched over a 40 mm outerdiameter mandrel. This tube serves as a cushion to aid in the subsequentlamination of the ePTFE material to the stent frame and is not part ofthe final device. Suitable expanded PTFE tubes for this use arecommercially available.

A “sacrificial film” is also used to facilitate the construction of theinventive device, serving as a release layer to aid in removal of thestent-graft from the cushion tube and mandrel and providing a radialforce to aid in bonding the ePTFE to the stent. The sacrificial film ispreferably one with high strength (or “retraction force”) that willwithstand the processing conditions. A suitable film is one made inaccordance with U.S. Pat. No. 3,953,566, incorporated by reference, thathas been sintered to maintain its dimensions during processing. Thisfilm is 25.4 mm and 50.8 mm wide, approximately 0.013 mm thick, andpossesses a matrix tensile strength of about 690 MPa in its highstrength (longitudinal) direction, tested as described above. It has adensity of about 0.2–0.3 g/cc. This film is not a part of the finaldevice. It should be noted that the PTFE films used in all the exampleshave all been subjected to temperatures exceeding the crystalline melttemperature of PTFE (“sintered”). One layer of this 25.4 mm wide film ishelically wrapped on top of the cushion tube with about a 10% overlap,creating a continuous layer. The tail end of this film is left exposedat both ends of the mandrel.

Helical wrapping facilitates later removal of this film. This film layeris unraveled from under the device at the end of the process by pullingon this tail, in order to facilitate the removal of the stent-graft fromthe cushion tube and mandrel.

Next, two layers of cover film are applied in a cigarette wrap fashionsuch that the high strength direction of the film is oriented along thelongitudinal axis of the tube, thereby creating a seam oriented alongthe entire length of the tube. One layer of the same cover film is thencircumferentially applied. That is, the film is rolled on top of theprevious layers such that the high strength direction of the film isoriented perpendicularly to the longitudinal axis of the tube. Thisprocedure also produces a seam oriented along the entire length of thetube, but is not transferred to the luminal surface. The stent frame isthen placed over the covered mandrel in such a way that the undulationsare aligned in phase. Next, an additional circumferential layer of thecover film is applied, followed by two layers of the cover film appliedlongitudinally. Finally, eight layers of 50.8 mm wide film of the sametype described above are applied in an up and back helical pattern. Thecushion tube is secured to the mandrel with bands of wire to preventlongitudinal shrinkage during subsequent heating. The sequence ofpreparing the device and the number and orientation of film layers forthis and other examples appear in Table 1. This table also describesproperties of the stent-grafts.

TABLE 1 Example 1 Example 3 Example 4 Example 6 Deployed ID 40 mm 26 mm31 × 13 mm 23 × 13 mm Wire 0.30 mm 0.20 mm 0.30 mm 0.20 mm DiameterNumber of 8 8 top of trunk: 8 top of trunk: 8 Apices leg: 4 leg: 4 Stent15 min- 15 min- 15 min- 15 min- Frame utes @ utes @ utes @ utes @Treatment 450° C. 450° C. 450° C. 450° C. FEP Heat n/a n/a n/a n/aTreatment Cushion OD = OD = OD = OD = Tube/ 40 mm 26 mm 31 mm 31 mmMandrel OD = OD = 13 mm 13 mm Inner 1 layer 1 layer 1 layer 1 layerRelease Film Inner Long. 2 layers 2 layers 2 layers 2 layers Film InnerCircum. 1 layer 1 layer 1 layer 1 layer Film Stent Frame wire wire wirewire Outer 1 layers 1 layers 1 layers 1 layers Circum. Film Outer Long.2 layers 2 layers 2 layers 2 layers Film Outer Comp. yes yes yes yesFilm Heat 40 min- 20 min- 30 min- 20 min- Bonding utes @ utes @ utes @utes @ 380° C. 380° C. 380° C. 380° C. Delivery 10 F: 6 F: 1.96/ 10 F:3.28/ 6 F: 1.96/ Tube 3.28/3.33 2.01 3.33 2.01 Dimensions 9 F: 2.92/ 9F: 2.92/ (in mm) 3.00 3.00 [ID/OD] Guidewire 0.89 mm/ 0.89 mm/ 0.89 mm/0.89 mm/ Diameter/ 10 F 6 F 10 F 6 F Delivery no wire/ no wire/ Profile9 F 9 F a:b 12.2:1 13.3:1 9.5:1 11.7:1 Ratio 13.7:1 10.6:1 Key: “n/a”indicates not applicable; “ID” indicates inner diameter; “OD” indicatesouter diameter; “Number of apices” indicates the number of exposedapices at an end of a graft; “Long.” indicates longitudinal; “Circum.”indicates circumferential; “Comp.” indicates compression; “Deliveryprofile” indicates smallest sized hole through which the compacteddevice plus delivery tube can fit; “a” indicates deployed dimension inmm; “b” indicates compacted dimension in mm.

The entire assembly is placed in an oven set to 380° C. for 40 minutes.The heat-induced retraction of the sacrificial film provides compressivebonding forces, thereby heat bonding the cover films, providing anintegral stent-graft. The assembly is removed from the oven and allowedto cool. The eight outer layers of sacrificial film are removed, thenthe single inner layer the sacrificial film is removed. Next, the deviceand cushion tube are removed from the mandrel, and the stent-graft andcushion tube are separated.

Expanded PTFE sewing thread (RASTEX® Expanded PTFE Thread, 1200 denier,available from W. L. Gore & Associates, Inc., Elkton, Md.) is tied toone end of the device in order to facilitate pulling the device througha 30° included angle, polymeric, smooth, tapered fixture (funnel) inorder to reduce the diameter. The device is successively pulled throughlonger funnels possessing the same inlet diameters (therefore,possessing smaller diameter outlets), thereby reducing its compacteddiameter. The device is compacted to its minimum diameter using afixture in which the small end of the funnel is mated with a capturetube that houses a thin-walled (approximately 0.025 to 0.038 mm wallthickness) polyester tube. This polyester tube is constructed byelongating a heated polyester shrink tube (item number 210100CST,available from Advanced Polymers, Inc., Salem, N.H.). The polyester tubeis employed to maintain the stent-graft in the non-distended state andserve as a delivery housing tube for the stent-graft. The diametricreduction is facilitated by chilling the nitinol-based device with arefrigerant spray (Freeze Mist, G C Thorsen, Inc., Rockford, Ill.)during draw-down through the tapered die. The final constrained deviceplus polyester delivery tube fit through a 10 F hole. The thickness ofthe bonded ePTFE covering is approximately 0.013 mm. The device ispulled from the polyester tube. Upon release from the tube, thestent-graft is warmed to about physiologic body temperature (35–40° C.)to deploy it. The device is radially compressed once again after a 0.89mm wire is inserted in the lumen of the device in order to simulate thepresence of a guidewire. The use of the term “guidewire” in the examplesand tables refers to such a spacer wire.

The device is once again captured inside a tube. The device plus apolyester constraining tube fit through a 10 F hole. Once deployed, thedevice self-expands in a 36° C. water bath to a 38 mm inner diameter.Gently pulling the stent-graft over a tapered mandrel increases itsinner diameter to 40 mm. Note that blood pressure applies a radial forcein vivo and self-expanding devices are typically subjected to balloondilatation once they are deployed. (Note that the stent-grafts in allexamples self-expand to the deployed diameters presented in Tables 1 and2, unless otherwise noted.)

The graft is once more compacted without a guidewire. This time thedelivered profile of the captured device is 9 F (that is, its dimensioninside a delivery tube). The stent-graft deploys (self-expands) to a 39mm inner diameter in a 40° C. water bath. Gently pulling it over atapered mandrel increases its inner diameter to 40 mm.

The a:b ratio for this device ranges from 12.2:1 to 13.7:1 and increasedwith successive pull-downs.

Foreshortening is a percentage defined as the change in length from thecaptured state to the deployed state divided by the length of the devicein the captured state, where the diameter of the device is at theminimum. The device is once again captured inside a 9F tube without aguidewire, as described above. The length of the device is measured inthe captured state at 7.68 cm. The device is deployed in a 36° C. waterbath. It deploys to a 40 mm. The length of the device is measured in thedeployed state at 7.62 cm. The device foreshortened 1%.

EXAMPLE 2

Another 40 mm inner diameter thoracic aortic stent-graft is constructedusing polyester as the stent covering material. The stent portion isconstructed using 0.20 mm diameter nitinol wire (SE 508; 40–45% coldworked; Nitinol Devices & Components, Fremont, Calif.). Yellow polyesterfilm (PES 30/25, available from Saatitech, Inc., Somers, N.Y.) isemployed as the stent covering. The polyester material is approximately0.046 mm thick. The stent member is formed and heat treated in themanner described above in Example 1. The stent covering is attached tothe inner surface of the stent frame with CV-8 Sutures (available fromW. L. Gore & Associates, Inc., Flagstaff, Ariz.), using a running stitchand tying the ends of the of the sutures together.

As in Example 1, the device is pulled down into a tapered fixture andcontained within a capture tube containing a removable polyester innerliner. A 0.89 mm guidewire is inserted inside the stent-graft prior tocompaction. A long tail of the polyester fabric material is used to pullthe stent-graft through the fixture. The inner and outer diameters ofthe delivery tube are approximately 3.94 and 4.01 mm, respectively. The40 mm stent-graft over a guidewire plus polyester tube (delivery tube)fit within a 12 F hole. The stent-graft deploys to 39 mm in a 36° C.water bath. It increases in inner diameter to 40 mm when gently pulledover a tapered mandrel.

The a:b ratio for this device is 10.2:1.

EXAMPLE 3

A 26 mm inner diameter thoracic aortic stent-graft is constructed using0.20 mm nitinol wire (SE 508; 40–45% cold worked; Nitinol Devices &Components, Fremont, Calif.) and ePTFE film. This stent-graft is made inthe same manner, with the same materials, as described in Example 1following the steps outlined in Table 1. The device is drawn down over a0.89 mm diameter wire to simulate the presence of a guidewire. Thestent-graft and wire are pulled into a polyester tube (fabricated asdescribed in Example 1). The stent-graft plus polyester tube fits withina 6 F hole. The stent-graft deploys to 24 mm in a 36° C. water bath.Gently pulling the stent-graft over a tapered mandrel deploys the deviceto 26 mm.

The a:b ratio for this device is 13.3:1.

EXAMPLE 4

The bifurcated stent-graft of the present invention consists of amodular design as described in PCT Application PCT/US98/27893 toThornton et al., incorporated by reference. This design incorporates amain body (i.e., trunk) component that incorporates the trunk, one leg,and a portion of the contralateral leg, as is illustrated in FIG. 4. Thecontralateral leg constitutes the other component. These two componentsare independently introduced into the vessels. The contralateral leg ispositioned inside the contralateral leg portion of the main bodycomponent. The geometry, hence volume, of the main body componentmandates that its delivery profile is always larger than that of the legcomponent. Achieving a percutaneously deliverable main body componentensures that the entire device can be percutaneously delivered.Consequently, only main body components are constructed for the purposesof this and other bifurcated stent-graft examples.

The main body component of a 31 mm (trunk inner diameter) by 13 mm (limbinner diameters) bifurcated stent-graft designed for the treatment ofabdominal aortic aneurysm disease is constructed using 0.30 mm nitinolwire and an expanded PTFE film. The stent portion is built using 0.30 mmdiameter, 40–45% cold worked NiTi (nitinol) wire (SE 508; NitinolDevices & Components, Fremont, Calif.) formed using a mandrel withprotruding pins as previously described. The stent is constructed usinga single wire, creating an undulating, helical, tubular, bifurcatedstent member by winding the wire on a pin fixture as previouslydescribed. This pattern includes in-phase nested apices that aid incompaction.

With the exception of steps required to accommodate the bifurcated shapeof the stent-graft, this stent-graft component is made in the samemanner, with the same materials, as described in Example 1 following thesteps outlined in Table 1.

The bifurcated section is constructed as follows. Y-shaped pin fixturesare used to construct the free standing stent frames and Y-shapedmandrel tooling is used to construct the stent-graft devices. As inother examples, a cushion tube is employed as a construction aid. Onelarge ePTFE tube is sutured to two smaller ePTFE tubes to form abifurcated cushion tube. Once placed on the mandrel the cushion tube iswrapped with sacrificial film with each leg of the construction wrappedindividually and an additional layer covering the trunk. Subsequentlayers of cover film are applied over the entire construction bridgingover the gap between the individual legs of the bifurcation. The coverfilm covering the two legs is applied loosely to allow seam sealing ofthe cover film between the legs to form the smaller tubes of thebifurcation. The seam is sealed by hand with a soldering iron set at400° C. As before, more sacrificial film is applied for compression heatbonding of the assembly. To apply the necessary compressive forcesbetween and around the legs of the bifurcation, scraps of cushion tubematerial formed into two wedges and covered with polyimide sheeting(0.03 mm thickness, 12.7 mm wide, #TKH-100, available from FralockCorp., Canoga Park, Calif.) are placed on both sides, between the legs,and under the sacrificial film bonding layer. Retraction forces of thesacrificial film during heat bonding forced the wedges into the spacebetween the legs thereby facilitating bonding the stent frame and graftcovering material together. After heat bonding, the sacrificial film andthe wedges are removed.

The stent-graft is compacted in the same manner as described inExample 1. The trunk portion is pulled into the die first. Thestent-graft plus 0.89 mm guidewire plus capture tube fit within a 10 Fdelivery tube. The stent graft deploys, it self-expands, to a 31 mminner diameter in a 36° C. water bath. The device is compacted andrestrained within a polyester tube again, this time without a guidewire.The delivery profile is reduced to 9 F. The stent-graft deploys(self-expands) to a 30 mm inner diameter in a 40° C. water bath. Gentlypulling it over a tapered mandrel increases its inner diameter to 31 mm.

The a:b ratio of this device ranges from 9.5:1 to 10.6:1.

EXAMPLE 5

Another main body component of a 31 mm (trunk inner diameter) by 12 mm(limb inner diameters) bifurcated stent-graft is constructed usingpolyester material as the stent covering material. The stent portion isconstructed using 0.20 mm, 40–45% cold worked NiTi (nitinol) wire (SE508; Nitinol Devices & Components, Fremont, Calif.). Yellow polyesterfilm (PES 30/25, available from Saatitech, Inc., Somers, N.Y.) isemployed as the stent covering. The polyester material is approximately0.046 mm thick. The stent member is formed and heat treated in themanner described above in Example 4. The stent covering is attached tothe inner surface of the stent frame with CV-8 Sutures (available fromW. L. Gore & Associates, Inc., Flagstaff, Ariz.), using a running stitchand tying the ends of the of the sutures together.

As in Example 4, the device is pulled down into a tapered fixture andcontained within a capture tube containing a removable polyester innerliner. A long tail of the polyester fabric material is used to pull thestent-graft through the fixture.

The delivery tube inner and outer diameter dimensions are 3.28 mm and3.33 mm, respectively. The stent-graft main body component plus 0.89 mmwire plus polyester tube (delivery tube) fit within a 10 F hole. Thestent-graft deploys to a 31 mm inner diameter in a 40° C. water bath.

The a:b ratio is 9.5:1.

The stent-graft is then compacted again without a guidewire. Thestent-graft is pulled into a delivery tube possessing inner and outerdiameter dimensions of 2.91 mm and 2.97 mm, respectively. Thestent-graft plus delivery tube fit within a 9 F hole and deployed(self-expanded) at 36° C. to 30.5 mm. Gently pulling it over a taperedmandrel increases its diameter to 31 mm.

The a:b ratio is 10.6:1.

EXAMPLE 6

A 23 mm (trunk inner diameter) by 13 mm (limb inner diameters)bifurcated stent-graft main body component is constructed using 0.20 mmdiameter, 40–45% cold worked NiTi (nitinol) wire (SE 508; NitinolDevices & Components, Fremont, Calif.) and ePTFE as the stent coveringmaterial. The stent member is formed and heat treated in the mannerdescribed above in Example 4. This stent-graft component is made in thesame manner, with the same materials, as described in Example 4following the steps outlined in Table 1.

As in Example 4, the device is pulled down into a tapered fixture andcontained within a capture tube containing a removable polyester innerliner. The stent-graft main body component plus 0.89 mm guidewire pluspolyester tube (delivery tube) fit within a 6 F hole. The device isdeployed, allowed to self-expand, in a 36° C. water bath. The trunkdeploys to an inner diameter of 21 mm. Gently pulling the stent-graftover a tapered mandrel increases its inner diameter to 23 mm.

The a:b ratio for this device is 11.7:1.

EXAMPLE 7

A 3.2 mm inner diameter stent-graft is created using ePTFE film and 0.10mm diameter, 40–45% cold worked NiTi (nitinol) wire (SE 508; NitinolDevices & Components, Fremont, Calif.). With the exception of the meansof attaching the film to the stent frame and the use of 6.35 mm wide asopposed to wider sacrificial film, this stent-graft is made in the samemanner, with the same materials, as described in Example 1 following thesteps outlined in Table 2. This table also describes properties of thestent-grafts of this and other examples.

The stent frame is powder coated with fluorinated ethylene propylene(FEP) powder (NC1500, available from Daikin Industries, Ltd., Osaka,Japan). FEP powder is placed and stirred in a kitchen blender to createa fine fog of FEP dust. The wire stent frame is cooled with arefrigerant spray, then placed in the fog, thereby coating the FEP tothe wire. The FEP is then heat bonded to the wire by placing the coatedstent frame into a convection oven set at 320° C. for 3 minutes. The FEPcoating enhanced later bonding of the cover film to the stent frame.

The device is pulled down into a tapered fixture and contained within acapture tube containing a removable polyester inner liner as describedin Example 1. The stent-graft plus 0.46 mm guidewire plus delivery tubefit within a 3 F hole. A 36° C. water bath is used to deploy thestent-graft. The device is deployed, then compacted again without aguidewire. This time the device plus capture tube fit within a 2.3 Fhole. The stent-graft is deployed again in the 36° C. water bath.

The stent-graft exhibits an a:b ratio ranging from 3.4:1 to 4.5:1.

TABLE 2 Example 7 Example 8 Example 9 Deployed ID 3.2 mm 2 mm 3 mmNumber of 4 3 8 Apices Wire 0.10 mm 0.10 mm [tube thick- Diameter ness =0.11 mm] Stent Frame 6 min- 6 min- 6 min- Treatment utes @ utes @ utes @450° C. 450° C. 450° C. FEP Heat 3 min- 3 min- 3 min- Treatment utes @utes @ utes @ 320° C. 320° C. 320° C. Cushion OD = OD = OD = Tube/ 3.2mm 2 mm 3 mm Mandrel Inner 1 layer 1 layer 1 layer Release Film InnerLong. 2 layers 2 layers 3 layers Film Inner Circum. n/a n/a 1 layer FilmStent Frame wire wire cut tube Outer 1 layer 1 layer n/a Circum. FilmOuter Long. 1 layer 1 layer n/a Film Outer Comp. yes yes n/a Film heatbonding 5 min- 4 min- 5 min- utes @ utes @ utes @ 380° C. 380° C. 380°C. Delivery 3 F: 0.94/ 2 F: 0.61/ n/a Tube 1.00 0.66 Dimensions 2.3 F:0.71/ 2.5 F: 0.76/ (in mm) 0.76 0.81 [ID/OD] Guidewire 0.46 mm/3 F nowire/2 F no wire/4.2 F Diameter/ no wire/ 0.30 mm/ Delivery 2.3 F 2.5 FProfile a:b 3.4:1 3.3:1 2.1:1 Ratio 4.5:1 2.6:1 Key: “n/a” indicates notapplicable; “ID” indicates inner diameter; “OD” indicates outerdiameter; “Number of apices” indicates the number of exposed apices atan end of a graft; “Long.” indicates longitudinal; “Circum.” indicatescircumferential; “Comp.” indicates compression; “Delivery profile”indicates smallest sized hole through which the compacted device plusdelivery tube can fit; “a” indicates deployed dimension in mm; “b”indicates compacted dimension in mm.

EXAMPLE 8

A 2 mm inner diameter stent-graft is constructed using 0.10 mm nitinolwire (SE 508; 40–45% cold worked; Nitinol Devices & Components, Fremont,Calif.) and an expanded PTFE film. This stent-graft is made in the samemanner, with the same materials, as described in Example 7 following thesteps outlined in Table 2. FEP is coated onto the stent frame in thesame manner as described in Example 7, as well.

The device is pulled down into a tapered fixture and contained within acapture tube containing a removable polyester inner liner as describedin Example 7 and Table 2. The stent-graft without a guidewire plusdelivery tube fit within a 2 F hole. The device is deployed in a 36° C.water bath, then compacted again, with a 0.30 mm guidewire. This timethe device plus capture tube fits within a 2.5 F hole. It deploys(self-expands) to a 2 mm inner diameter in a 40° C. water bath.

The a:b ratio for this stent-graft ranges from 2.6:1 to 3.3:1.

EXAMPLE 9

For this example a section of nitinol tubing (0.11 mm wall thickness,1.30 mm outer diameter, available from Nitinol Devices & Components,Fremont, Calif.) is machined into a configuration similar to the helicalpattern of serpentine bends of wire in the other examples. The stentelement 170 is illustrated in FIG. 28. The stent pattern is cut from thenitinol tube using a NdYag laser (available from Laserage, Waukegan,Ill.). The laser removes material from the tubing to leave only aframework skeleton that serves as the stent frame. The laser machinedtube is then chilled with a refrigerant spray and stretched up on atapered mandrel to achieve a 3.0 mm inner diameter.

The stent frame is next subjected to the stent frame (heat) treatmentdescribed in Table 2, then quenched in water, in order to set the stentframe at this larger, deployed state, diameter. The stent frame is thenFEP powder coated in the same manner as described in Example 7. Thegraft is then fabricated and attached to the stent frame in the samemanner, with the same materials, as described in Example 7 following thesteps outlined in Table 2.

This self-expanding stent-graft device is pulled down into a taperedfixture and capture tube as described in Example 7 and Table 2, withouta liner inside the capture tube. No guidewire is inserted into the lumenprior to compaction. The stent-graft is pulled by grasping a portion ofuntrimmed covering material extending beyond the end of the stent frame.The stent-graft without a delivery tube fit within a 1.4 mm hole. Thestent-graft is deployed from the capture tube at ambient temperature andexpands to a 3.0 mm inner diameter.

The a:b ratio for this stent-graft is 2.1:1.

EXAMPLE 10

Commercially available 26 mm and 40 mm inner diameter thoracic aorticstent-grafts (Thoracic EXCLUDER™ Endovascular Prosthesis, W. L. Gore andAssociates, Inc., Flagstaff, Ariz.) are also subjected to some of theinventive compaction techniques to determine if their delivery profilescould be reduced beyond current compacted dimensions. Presently, themanufacturer suggests that Introducer sheaths sized 22 F and 24 F beused with these 26 mm and 40 mm devices, respectively.

The outer sealing cuffs are removed from these devices prior to anytesting. A 26 mm device without any wire inserted into its lumen, ispulled through a funnel-shaped tapered die into a capture tube asdescribed in Example 1, except that a two part tapered die is used andand no delivery tube liner is present inside the capture tube.

As is illustrated in FIG. 29, a two part die 172 is employed having afirst stage funnel section 174 and a second stage funnel section 176.The first stage section 174 has an included angle of 12°, the secondstage section 176 has an included angle of 12.4°. The device is pulledinto successively smaller capture tubes 178. Containment within a 3.43mm capture tube indicates that it will fit within an 11 F hole. A 36° C.water bath is used to deploy the stent-graft.

The graft is deployed to 24 mm, increasing to 26 mm when gently pulledover a tapered mandrel.

Another 26 mm device, also without a guidewire, is pulled through afluted tapered die, thereby fitting into a 3.18 mm capture tube, henceit fit within a 10 F hole. The second stage section 176 is modified tocreate flutes in the manner previously described with reference to FIGS.16 a through 16 c. Eight (8) flutes are created, matching the number ofapices of the device.

Using the fluted compaction techniques previously described, thedelivery profile of the 26 mm devices is reduced by 1 F. A 36° C. waterbath is used to deploy the stent-graft. The graft is deployed to 24 mm,increasing to 26 mm when gently pulled over a tapered mandrel.

The use of the fluted die increases the a:b ratio from 7.6:1 to 8.2:1.

The 40 mm device without a guidewire is subjected to the same compactionprocess using a two part smooth tapered die as described in FIG. 29. Thefirst stage section 174 and second stage section 176 have includedangles of 12° and 7.2°, respectively. The device is successively pulledinto capture tubes 178 possessing inner diameters of 6.35 mm 6.00 mm,and 5.33 mm. The size of the device precluded it from being drawn into a5.00 mm inner diameter capture tube. This 40 mm device is subsequentlypulled through the 5.33 mm capture tube a total of five times to prepareit for pulling into a smaller capture tube. The force required to pullthe device through this capture tube decreases from 27 kg for the firstpull to 18 kg for the last pull. The decrease in force suggests that thedevice could be pulled into a smaller capture tube without damaging thedevice. The device is then successfully pulled into a 5.00 mm capturetube. This step of repeatedly pulling the stent-graft through a samesized capture tube enables it to be compacted further.

The a:b ratio for this stent-graft is 8:1.

While particular embodiments of the present invention have beenillustrated and described herein, the present invention should not belimited to such illustrations and descriptions. It should be apparentthat changes and modifications may be incorporated and embodied as partof the present invention within the scope of the following claims.

1. A method of compacting an endoprosthesis into a compacted dimensioncomprising providing a self-expanding endoprosthesis comprising astent-element; providing at least one internally tapered dieproportioned to compact the endoprosthesis, the tapered die includingmultiple raised flutes and grooves therein to define a tapered surface;passing the endoprosthesis through the tapered die to reduce itsdimensions, the raised flutes and grooves causing the endoprosthesis tofold into uniform pleats in its compacted dimension.
 2. The method ofclaim 1 that further comprises passing the endoprosthesis through thetapered die at least one additional time.
 3. The method of claim 2 thatfurther comprises allowing the endoprosthesis to expand before passingit through the at least one tapered die at least one additional time. 4.The method of claim 1 that further comprises subsequently passing theendoprosthesis through a second taper die having a smaller diameter. 5.The method of claim 1 that further comprises passing the endoprosthesisthrough a tapered die having a larger diameter prior to compacting inthe at least one tapered die.
 6. The method of claim 1 that furthercomprises providing the stent-element with forward facing apices andrearward facing apices; providing a tether line attached to or alignedwith one or more of the apices; pulling the endoprosthesis through theat least one tapered die using the tether line.
 7. The method of claim 6that further comprises providing an actuation mechanism; attaching thetether line to the actuation mechanism to pull the endoprosthesisthrough the at least one tapered die.
 8. The method of claim 6 thatfurther comprises providing multiple tether lines; aligning the tetherlines with only forward facing apices so that when the tether lines arepulled through the grooves only the forward facing apices are visible onthe outside of the compressed endoprosthesis.
 9. The method of claim 1that further comprises positioning the flutes evenly around the tapereddie so as to produce a uniform spacing of pleats around the compressedendoprosthesis.
 10. The method of claim 9 that further comprisesproviding a uniform spacing of grooves within the at least oneendoprosthesis; providing a tether line to correspond with each groove;and passing the endoprosthesis through the tapered die using the tetherlines.
 11. The method of claim 1 that further comprises cooling theendoprosthesis prior to passing through the tapered die.